The present invention relates to an electromagnetic directional control valve for transferring the motion of an iron core, movable upon excitation of a solenoid coil, to a spool and for switching between fluid passages of a valve main body and, more particularly, to an electromagnetic directional control valve for detecting whether a magnetic field which drives the movable iron core has been generated by the application of a DC voltage to the solenoid coil.
FIG. 1 shows a cross sectional view of a conventional electromagnetic directional control valve.
In FIG. 1, reference numeral 10 denotes a valve main body operable for switching between fluid passages; 12 indicates an electrical equipment box to which a cable for supplying an electric signal from the outside is connected; and 14 represents a solenoid section.
A spool 16 is assembled into the valve main body 10 so as to be slidable in the axial direction. The spool 16 is held at the neutral position shown in the diagram by springs 18-1 and 18-2 arranged on both sides of the spool 16. The passage in the valve main body 10 can be switched by moving the spool 16 to the right or left of the neutral position.
The solenoid portion 14 arranged on the left side of the valve main body 10 has a casing 20 made of a synthetic resin material. A coil 22 is assembled in the casing 20. The coil 22 is enclosed in a box-shaped coil frame 26 made of a permeable material in a state in which the coil is wound around a coil bobbin 23. A core tube 25 is provided in the coil frame 26. A movable iron core 24 is assembled in the core tube 25 so as to be movable in the axial direction. A fixed iron core 28 is arranged and fixed on the right side of the movable iron core 24 at a predetermined distance therefrom. A through hole is formed in the fixed iron core 28 in the axial direction. A push pin 30-2 is pierced into the through hole. The right end of the push pin 30-2 is coupled with the spool 16 and the left end is coupled with the movable iron core 24.
The right end of the core tube 25 is fitted into the hole formed in the edge surface of the valve main body 10 and is fixed by attaching a flange 35 to the valve main body 10 by using a screw 37. On the other hand, a plug 27 is fitted from the inside of the core tube 25 into the hole formed therein on the left side of the core tube, thereby closing the left side of the core tube.
A terminal plate 32 is provided in the electrical equipment box 12 attached on the valve main body 10. The cable led in from the outside is connected to a terminal of the terminal plate 32. A DC voltage is applied to the coil 22 provided in the solenoid section 14 through a signal line from the terminal plate 22, thereby exciting the coil.
An indicator lamp 34 which can be observed from the outside is also provided in the box 12. When a DC voltage is applied from the outside to excite the coil 22, the indicator lamp 34 is lit to indicate that the electromagnetic valve has operated.
According to the operation of such a conventional electromagnetic direction control valve, when the coil 22 of the solenoid section 14 is excited by supplying a DC power source from the outside, the movable iron core 24 is driven to the right by the magnetic field generated from the coil 22. The spool 16 is pushed by the push pin 30-2, thereby switching the passage in the valve main body 10.
At this time, the indicator lamp 34 provided in the electrical equipment box 12 is lit to indicate the operation of the electromagnetic directional control valve. However, even if the indicator lamp 34 is lit, it is impossible to check whether the coil 22 had actually been excited and the spool 16 actually moved.
To check whether the spool 16 has been moved to the correct position or not by the excitation of the coil 22 as mentioned above, hitherto, a microswitch 38 has been provided in a cover 36 on the right side of the valve main body 10. A push pin 30-1 coupled to the right side of the spool 16 is arranged so as to face a switch knob 40 of the microswitch 38. The indicator lamp 34 is lit by the actuation of the microswitch 38.
Therefore, when the movable iron core 24 is moved to the right upon application of the DC magnetic field generated by the excitation of the coil 22 and the spool 16 is moved by the push pin 30-2, the push pin 30-1 coupled with the right side of the spool 16 pushes the switch knob 40 to thereby actuate the microswitch 38. The indicator lamp 34 is lit upon actuation of the microswitch 38, so that it is possible to confirm that the spool 16 has operated properly.
When the current supply to the coil 22 is stopped, the spool 16 is returned to the neutral position shown in the diagram by the forces of the springs 18-1 and 18-2.
However, the conventional electromagnetic directional control valve, which utilizes a mechanism for checking the operation of the valve by detecting the motion of the spool 16 by way of microswitch 38, has the following problems.
First, in the electromagnetic directional control valve in which the solenoid section 14 is attached on one side, for instance, the left side of the valve main body 10 as shown in the diagram, causes the overall size of the electromagnetic direction control valve to be larger than would otherwise be necessary. This will, in turn, require an enlarged area for installation of the valve.
Also, since the spool 16 is required to push the switch knob 40 of the microswitch 38, it is necessary that sufficient force is generated to depress the switch knob 40.
Further, the spacing between the push pin 30-1 and the switch knob 40 must be correctly adjusted so that the microswitch 38 is actuated when the spool 16 reaches a predetermined position. This spacing adjustment is complicated.
In addition, since the microswitch 38 is provided on one side of the valve main body 10, it is impossible to realize a construction in which the solenoid sections are attached to both sides of the valve main body 10 and, thus, in which the spool is switchable between three positions such as those which define straight, neutral and crossed fluid passages. That is, such a construction limits the valve to a two-position valve.